1. Field of the Invention
The present invention relates to a two-stage compression heat pump system adapted to perform cooling and heating in a single unit, which performs a single-stage compressing operation in summertime and a two-stage compressing operation in wintertime, and which has a separate intercooler for controlling the system to provide optimum intermediate pressure, and a device for protecting a high-stage compressor through the control of a fluid-level inside a flash tank.
2. Background of the Related Art
Generally, a conventional system for performing cooling and heating in single unit is either a system having an air conditioner (or a chiller) and an electric heater, or a heat pump type air conditioner having one compressor.
However, in the former case where an air conditioner (or a chiller) and an electric heater are assembled in one package, excessive energy is consumed for heating. Even in the latter case of the heat pump type air conditioner that can save energy, if the temperature of a heat source is decreased in wintertime, such a system operates at an excessive compression ratio together with decreased evaporation pressure, and thus the operating efficiency of the compressor is lowered, and heating capacity is decreased due to the decrease of refrigerant mass flow rate in the system, thereby lowering system efficiency. In addition, if the evaporation pressure of the system is decreased, the compressor discharge gas temperature can be increased excessively, so that the system can be adversely influenced in terms of safety.
A two-stage compression system can exhibit excellent performance compared with conventional systems. However, conventional flash tanks do not have a device for detecting or removing fine droplets generated in the process of heat balance when refrigerant gas and a two-phase flow state are mixed, where the refrigerant gas is superheated vapor discharged from a low-stage compressor and the two-phase flow refrigerant, passed through an intercooler, has a liquid portion. Therefore, inflow of the fine droplets into a high-stage compressor cannot be blocked. Furthermore, an appropriate method of collecting refrigeration oil from the flash tank to the compressor has not been proposed, the refrigeration oil therefore being contained in the refrigerant gas from the low-stage compressor.